Considering the extremely vast field of application of this type of materials, many teams have focused their research on methods for elaborating such materials.
A first strategy consisted of impregnating polymeric materials with metal salt solutions.
Thus, Rinde et al. in U.S. Pat. No. 4,261,937 describe a method for preparing polymeric foams doped with a metal element, consisting of pouring a polymeric gel into an aqueous solution comprising a salt of said metal element. The gel is then put into the presence of a series of solvents with decreasing polarity, in order to remove the introduced water. Each solvent used should be capable of solubilizing the preceding solvent and is saturated by the selected metal salt.
This method however has the major drawback that the distribution of the metal element cannot be perfectly homogeneous at an atomic level, since crystallization phenomena of metal salts occur upon drying which is followed by the formation of nano- or micro-crystals in the material. On the other hand, because impregnation is achieved on a polymeric gel, diffusion of the metal elements does not occur in the totality of the gel.
Other authors have used alternatives of this type of strategy.
Thus, Mishra et al., in Plasma Phys. Control. Fusion 43 (2001) 1723-1732, describe the preparation of polystyrene microballoons doped with ultra-fine metal particles comprising the following steps:                a step for forming an emulsion comprising an aqueous phase and an organic phase comprising polystyrene, in which ultra-fine metal particles are dispersed;        a step for dispersing the aforementioned emulsion into a second aqueous phase, by means of which a triphasic emulsion is obtained;        a step for removing the organic phase, letting polystyrene balloons subsist, doped with metal particles, containing water;        a step for drying said polystyrene balloons.        
A second strategy consisted of no longer doping the materials after polymerization of the latter, but of acting upstream from the polymerization step by putting the metal element in contact with the polymerization medium, notably by using monomers bearing the desired dopant metal, depending on whether the metal is an integral part of the monomer molecule (in which case one refers to metal monomers) or is bound to the latter by means of a complexation reaction.
Thus, certain authors have focused their research work on the synthesis of vinyl monomers comprising metal elements or capable of being doped with metal elements, such as titanium.
This is the case of Miele-Pajot et al., in J. Mater. Chem., 1999, 9, 3027-3033, who describe the formation of a titanium complex obtained by reaction of a titanium alkoxide, titanium tetraisopropoxide, with cis-but-2-ene-1,4-diol HO—CH2—CH═CH—CH2—OH, which complex is then put into contact with a polymerization medium comprising styrene and divinylbenzene, in order to obtain polystyrene foams doped with titanium. However, the embodiment described in this document has the following drawbacks:                the titanium complex is unstable in an aqueous medium and notably in the polymerization medium, this instability may be expressed by cleavage of the metal-ligand bond;        the titanium complex thus degrades, during the polymerization of the latter with styrene and divinylbenzene, thereby generating low incorporation of titanium in the final polymeric material, the titanium mass percentage of the polymeric materials not exceeding 1.5%.        
Therefore there exists a real need for coordination complexes, which are stable in an aqueous medium, and notably when they are put into the presence of a polymerization medium and consequently with which polymeric materials doped with metal elements may be obtained, the doping level of which is controlled and is, because of the stability of the applied complexes, directly related to their introduction level in the polymerization medium.